The present invention relates to an improvement in horizontal axis, high speed wind generators (aerogenerators) of the type which use an air foil design for the blades and generally from two to four blades in a propeller type configuration to produce rotational motion.
More particularly, the present invention relates to an improved blade angle control for wind generators of the above-noted type.
Wind engine blade wheels are generally of three types. The first two types are designed to operate at very low speeds and are characterized by a blade wheel that has a relatively large blade surface area. This first category of low speed wind engine is the well known "Dutch" wind mill design. The "Dutch" wind mill is highly inefficient and unsuitable for high speed operation. Furthermore, since it has high torque characteristics, low speed start-up is not a significant problem.
The second type of low speed wind engine has been used in this country primarily for the pumping of water and U.S. Pat. No. 458,070 is representative thereof. Since low speed pumping windmills might have sixteen or more blades and are designed to operate at very low speeds under the effect of very low wind forces, no problems exist with respect to start up of such wind motors. Thus, governors need only be provided for adjusting the blade angles ("feathering") to prevent overspeeding. However, such wind motors are not suitable for use in generating electricity since they cannot be operated at the high velocities necessary for efficient electricity generation.
Accordingly, a third, propeller type of blade wheel has been utilized for electricity generation purposes. Such wind generators use an air foil design for the blades and generally from two to four blades to produce rotational motion. Reference can be made to U.S. Pat. Nos. 1,648,837, and 2,248,218 for typical examples thereof. Wind powered electrical generating wheels are designed for operation in the ten to twenty mile per hour windspeed range and are provided with a blade angle governor for preventing overspeeding and for producing a relatively constant speed wheel rotation in said 10-20 mph. wind range.
However, when such wind generators are designed for maximum efficiency in their normal operating range, difficulties arise in starting of the windmill, especially at low wind speeds and when a hydraulic system is utilized to transmit the power from the blade wheel at the top of a tower to its base. The reason for this is that the torque needed to start the blades moving is high, and such propeller type rotors are efficient low torque designs, relative to the above-noted pumping type wheels, due to the difference in exposed blade surface area and designed tip speed ratios of the blades, and this start-up torque problem is further compounded by the torque needed to drive the hydraulic system, especially in cold weather.
Accordingly, it is an object of the present invention to design a wind generating system which appreciably solves the problem with respect to obtaining enough torque for system start up, even in combination with hydraulic systems.
It is a further object of the present invention to solve the start-up problem without the use of auxiliary starter mechanisms, and without affecting normal operational efficiency.
These and other objects are achieved according to the present invention by providing an aerogenerator that has a governing device for the blades which maintains the blades of the rotor wheel at a first angle with respect to the wind so as to create a lower tip speed ratio than would be optimal under normal operating conditions until at least minimal operating conditions are achieved at which time the blade angle is quickly shifted into its normal operating, high efficiency position where it is retained, unless high winds occur, in which case the blades are progressively feathered to prevent overspeeding.
According to a preferred embodiment, the above-noted blade angle adjustment is obtained by pivotally connecting the blades between a pair of parallel spaced plates such that the blade angle is adjusted in accordance with the relative spacing of the plates, a first biasing mechanism being utilized to provide start-up governing control, while a second biasing arrangement is utilized to prevent overspeeding.
These and other features of the present invention will become further apparent from the following detailed description thereof and with reference to the accompanying drawings.